Audio Bitrates

Discussion in 'iPod' started by mrgreen4242, Sep 13, 2005.

  1. mrgreen4242 macrumors 601

    mrgreen4242

    Joined:
    Feb 10, 2004
    #1
    I decided to check out the new VBR option in iTunes 5 along with the Apple Lossless codec that I haven't used at all yet... I encoded the same song (Skellig by Loreen McKennit) in Lossless format, AAC 96kbps VBR, AAC 128kbps CBR (iTMS format), and AAC 256kbps CBR.

    I then loaded them onto my 1G iPod mini in a playlist, went into a fairly quiet room and listened to them all with the standard iPod headphones (quite a new pair, they came with a shuffle, not the iPod I was testing with). I then rated each song according to the apparent audio quality by giving each track a star rating. After syncing the iPod up to my computer, I looked at the rating I gave each track and it's bitrate.

    My results ended up putting them in this order, from highest to lowest:
    256kbps AAC CRB
    96kbps AAC VBR
    128kbps AAC CBR
    Apple Lossless

    This leads me to believe that I cannot hear the difference between 96kbps VBR AAC and the source media. I wonder how common that is? Does anyone else have any anecdotal evidence of how low quality music they find indistinguishable from the original?
     
  2. BlizzardBomb macrumors 68030

    BlizzardBomb

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    #2
    I noticed this too. A 96kbps VBR still sounds brilliant. I think this would be excellent if I ever got a Nano! Oh btw, if you encoded a song from 128kbps -> 256kbps, it would wield no difference. You can't get more quality from something that isn't even there.
     
  3. Lacero macrumors 604

    Lacero

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    Jan 20, 2005
    #3
    I am going to test out using 64KBps VBR AAC for songs on the shuffle. I think it'll still sound great (considering gym & street noises will drown out any artifacts) and I can pack in twice the number of songs.
     
  4. BlizzardBomb macrumors 68030

    BlizzardBomb

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  5. Lacero macrumors 604

    Lacero

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  6. Loge macrumors 68020

    Loge

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    #7
    Am I missing something here - Apple lossless is lowest ??
     
  7. Blue Velvet Moderator emeritus

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    Jul 4, 2004
    #8

    Could have something to do with it although how anyone can rate a low-bitrate lossy file higher than a lossless file is extremely puzzling.
     
  8. Lacero macrumors 604

    Lacero

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    #9
    Probably because in terms of filesize vs audio quality, it probably wasn't worth it, so it came in dead last.
     
  9. mrgreen4242 thread starter macrumors 601

    mrgreen4242

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    Feb 10, 2004
    #10
    My ratings were how I ranked them in a blind listening comparison. Not the 'true' or actual quality of the file. It also had nothing to do with the size of the file, it was completely blind.

    My point was the MY ears couldn't hear the difference from the 96kbps VBR file and the lossless. I have fairly poor hearing due to lots of loud noise exposure in the military and other recreational activities (shooting ranges, loud concerts, etc).

    I am aware of this. The files I listened to were all ripped directly from the CD to the various formats.

    I wish iTunes had a feature (and I was just talking about this in another thread) that kept a smaller version of the file "wrapped up" in the larger file for iPod checkout. I would MUCH rather have 96kbps VBR AACs on my iPod than anything else so I could squeeze an extra 25% more tracks into the same device.

    I have a feeling that the introduction of the VBR option is a precursor to something like this, though.
     
  10. dubbz macrumors 68020

    dubbz

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    Sep 3, 2003
    Location:
    Alta, Norway
    #11
    I can do something similar with my iRiver + custom firmware (although not with AAC). ;)

    Interesting test, in any way. I'm thinking that Apple might have been doing more improvement to the encoder, in addition to adding their kind of VBR.
     
  11. mrgreen4242 thread starter macrumors 601

    mrgreen4242

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    Feb 10, 2004
    #12
    Hm, I wonder if it would be possible to create a new user account, import the whole iTunes library from your main account, convert it to 96kbps VBR AAC, and then use that account to sync your iPod. With fast user switching it wouldn't be too much of a hassle really, and the "extra space" on your iPod might make it worth while.
     
  12. Blue Velvet Moderator emeritus

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    Jul 4, 2004
    #13
    Here's one workaround. Do what I do and use Doug's iTune Library Manager.

    This lets me have two libraries (or more if you pay): one all Lossless for home listening and the other all 256 AAC synced to the iPod.
     
  13. Cinematographer macrumors 6502a

    Cinematographer

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    far away
    #14
    I once made a blind listening comparison myself with a few friends. Five out of six times they said the 128 kBit/s-AAC files sounded better than the original songs from CD. ;)

    I don't see the point in investing hours and hours just to get an extra bit of quality that's impossible to detect by human ears.
     
  14. Blue Velvet Moderator emeritus

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    Jul 4, 2004
    #15
    Impossible? I think not. It depends on the type of music you listen to, your equipment and the volume you play it at... and nobody said anything about investing hours and hours in anything.

    To me, the difference between a 128AAC file such as the type that iTMS sells and a Lossless file is as clear as night and day.
     
  15. mrgreen4242 thread starter macrumors 601

    mrgreen4242

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    Feb 10, 2004
    #16
    You must have excellent hearing. MOST people can't tell any difference at all with the from CD to 128AAC. If they can it's only if they are really trying. Based on your previous post indicating that you use 256AAC for your iPod it must be very apparent to you or you wouldn't effectively half your iPods capacity.

    I wonder if there is a gender breakdown in this, and if so, is it caused by innate hearing superiority or if one sex is predisposed to do more damage to their hearing. If the former, it wouldn't suprise me. Women, for example, generally have better color vision than men. Only a tiny fraction of women are color blind, compared to some absurdly high number of men who have some form of color vision deficiency. On top of that, some women have the ability to see a "4th color", which amounts to a near infra red shade, that no man will ever see.

    If the latter, I wouldn't be suprised either. Most hearing damage is caused in our youth, and the young ladies that I know are generally much more sensible than the men.

    Thanks for that library link, btw, that is just what I was looking for. I am going to do a few tests of converting 128AAC and 160MP3 (what my library currently is in) files to 96VBR AAC and see how it sounds (CD directly to 96AAC may sound entirely different than 128 to 96 does). I suppose this means I will have to FairPlay my iTMS purchases?

    I wonder if we have been training ourselves over the last 10 years to 'prefer' lossy compressed music? Perhaps we have been listening to it long enough that the distortions introduced by the compression process are what we are expecting to hear now, and as such we pick it out as being "normal" compared to CDs? Did the friends you tested with listen to primarily compressed music? I've been using mp3's since abotu '95 or so, and rarely listened to CDs during that period.
     
  16. Blue Velvet Moderator emeritus

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    Jul 4, 2004
    #17
    It's all about listening, not hearing. :)

    But good headphones are far more revealing than the standard iPod buds.

    My vision is good for a 42-year old but sense of smell and taste is pretty poor compared to some of my friends -- and no, I'm not a cigarette smoker.
     
  17. mrgreen4242 thread starter macrumors 601

    mrgreen4242

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    Feb 10, 2004
    #18
    If you can't hear (well) no amount of listening is going to help. :) I do buy that good headphones are a huge part of it, which is one of the reasons I haven't sprung for an expensive set yet. :D

    I would like a set of those noise cancelling in ear headphones, though... good thing I don't have $200 burning a hole in my pocket. :p
     
  18. jholzner macrumors 65816

    jholzner

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    #19
    What are the file size differences betweent 128 vbr and 128 cbr. Also, between 96 vbr and 128 cbr?

    Thanks
     
  19. Cinematographer macrumors 6502a

    Cinematographer

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    #20
    That's an interesting theory. To your question: No, my friends used to be listening to CDs and radio, never to mp3s. They were very proud of their bang & olufsen stereo set and quite confident, they would hear (listen? :D ) the difference between the original track and the AAC-file played by the Pod.
     
  20. Cinematographer macrumors 6502a

    Cinematographer

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    #21
    As far as I know, that depends on the complexity of the music you're encoding. Take an audiobook and VBR will save you a lot of disk space. Take a piece of classical music and you won't see a big difference.
     
  21. NicP macrumors 6502

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    Jun 14, 2005
    #22
  22. mrgreen4242 thread starter macrumors 601

    mrgreen4242

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    Feb 10, 2004
    #23
    In theory (well, this comes from knowledge of the mp3 format, but I ASSUME that it holds for AAC as well) the 96kbps VBR should be 3/4 the size of 128kbps CBR in all circumstances.

    VBR is often, and more accurately, referred to as ABR or Average BitRate. The idea is that the overall file will have a size of, in this example, 96 kilobits per second. However, each individual second (or actually fraction of a second) can be any actual bitrate. So a fairly complex segment of a song, say a chorus in the middle of the track with sevearl instruments and a couple vocal tracks, may actually be 160kbps. However, the bits at the beginning, end, and during any sort of solo bridge where the sound is 'less complex' may actually only have a bitrate of 60kbps. All these will add up to an average that gives you a files size consistant with a 96kpbs CBR file, but with generally better quality.
     
  23. mrgreen4242 thread starter macrumors 601

    mrgreen4242

    Joined:
    Feb 10, 2004
    #24
    That was tremendoulsy interesting. I would like to note that the test in my original posting of this thread was for a song which is anything but pop, involves scores of instruments, none of which, I believe, is an electric guitar, and was also an independantly produced and released by the artist so, hopefully avoids any of the studio influenced crappy production practices.

    Given all that, I just couldn't hear the differences. I am going to retry this test with some better headphones when I get home, and I am also going to add another track to the test, this time something with a single accoustic guitar and a single vocal track, and see how that goes.
     
  24. Artful Dodger macrumors 68020

    Artful Dodger

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    #25
    Hi mrgreen4242,
    I can notice a nicer sound as I bought different headphones and I like some didn't spend a lot but enough to make it a difference. I think mine were $30-40 and it seems like a nice balance. I too have been exposed to loud sounds but not that much of a loss for me...at least I think (looks to see if someone is talking). But even with my friends Sony headset $20 has a better sound to me then the stock buds.
    When you did the tests how was the EQ setup? just wondered if this would make a difference for your tests. Anyway nice thread about this ;) i may have to do some just out of being curious.
     

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